1. "carrying a state" means when your opponent want to add a cube to the state you currently carry. He must do a support check. But if you have less than 4 cubes there, he may use his CP to eliminate your cubes without a supporting check.
2. The only benefit from "carrying a state" is to make your opponent do a support check when they want to crash you. When caculate the votes at the end, "4 cubes in a state" is as same as "1 cube in a state".
Correct. Carrying a state simply makes it harder for your opponent to remove your cubes from that state, since as you mentioned, a support check must be made. The number of cubes in each state is irrelavent when calculating votes. 1 is a good as 4.
3. You must eliminate the opponent's cubes first, then add your cubes, You can't use your CPs to replace your opponent's cube with yours.That means 1 CP can use to eliminate 1 opponent's cube,but can't use to eliminate 1 opponent's cube and add 1 cube of mine at the same time.
Correct, for 1 CP, you can only remove 1 opponent cube. It would take 2 CP to remove his then place your own.